The present invention relates to a weather-resistant coat formed on members made of aluminum or aluminum alloys such as car wheels, and to an aluminum member provided with such a weather-resistant coat.
Car wheels are conventionally produced by steel, but in order to reduce the weight of the automobiles, or to improve their appearances or designs, increasingly more attention has been paid to aluminum wheels. In general, aluminum wheels are coated with compositions for improving their weather resistance and corrosion resistance.
Weather-resistant coatings of aluminum wheels can be made in many ways, and they have conventionally been produced by so-called organic solvent-type coating compositions in order to improve the smoothness and clearness of the wheel surfaces. However, because of the increasing attention towards environmental problems, regulation of organic solvents' emision has become strict. Accordingly, it has become difficult to use the conventional organic solvent-type coating compositions.
Under these circumstances, powder coating for aluminum wheels has attracted much attention, especially in the United States where it became the leading method. In the United States, powders of polyester resins such as triglycidyl isocyanurate-based polyesters are widely used. Recently, there has been increasingly higher demand on coatings for aluminum wheels having better corrosion resistance. Weather resistance and paintability have also become desirable, but the above polyester-based powder coating fails to satisfy such demands.
In particular, so-called metallic coating tends to discolor, since it contains fine aluminum powder. In addition, the metallic coating shows poorer weather resistance than solid color coating. In view of these facts, a metallic coating composition for aluminum members having good weather resistance is demanded.